Re: Fly rigging?
Those links I posted are good starting points, but depending on where you live and what water you fish is going to determine how you use the set-up.
I never fish with more than two flies because, for one, it is actually illegal in Arizona. I also would rather fish one dry fly effectively than worry about droppers and tag ends, etc.... when I should be focusing on currents and drifts.
On some waters, two flies makes a more effective rig. For instance, the San Juan river. I played around with single and two fly rigs because I wanted to see for myself if the attractor did anything, after all, most fish won't move very far to take a small little midge. But two flies was definitely more effective than one, the attractor aspect of an annelid or a second midge definitely draws attention from the fish.
I only use three methods to fish two flies: occasionally I will leave my tag end long on the first fly and attach a second. Most of the time with a hopper dropper I'll add a bit of tippet to the bend of the hook and tie a nymph, or very rarely, second dry fly off of that. And sometimes (I tried this on the San Juan) I will, as tbloom suggested, drop the second fly off of the eye of the first fly with a length of tippet, provided I am fishing fine enough tippet and a large enough first fly that it will fit smoothly.